PHYSICOCHEMICAL PROPERTIES AND JUVENILE PHENOLOGY OF AFRICAN WALNUT (Plukenetia conophorum Muell Arg) ACCESSIONS FROM SOUTHEASTERN NIGERIA

ABSTRACT

African walnut (Plukenetia conophorum Muell Arg) is a member of the family Euphorbiaceae. It is cultivated principally for the nuts which are eaten raw or served as snacks after roasting or boiling. P. conophorum serves many nutritional and medicinal purposes as well as good source of rural income. Despite the potentials of this plant, its existence is threatened by deforestation, urbanization and similar activities. The present study was designed in an attempt to salvage this useful plant from extinction and provide basis for its conservation. Four accessions of P. Conophorum were collected from Abia, Anambra, Enugu and Rivers states, southeastern Nigeria. The objectives of the research were to evaluate the effects of three manure rates on juvenile growth stage of the accessions; determine the amino acid profile of the kernels and investigate possible bio-diversity among the accessions with respect to the seed physical traits and proximate components. Four specific experiments were conducted to achieve the set objectives. Seed physical traits (edible portion, pulp weight, seed volume, seed weight, pulp (kernel) weight, seed circumference and seed coat thickness) were measured. Standard laboratory procedures were employed in determining the proximate composition (moisture content, ash, fat, crude protein, fibre and carbohydrates) and amino acids profile of raw and boiled kernels. A pot experiment was set up to evaluate the seedling emerpgence and growth responses to three level of pig manure applications (0, 5. and 10t/ha). Data were collected on days to seedling emergence, emergence percentage, vine length, vine base girth, number of leaves per plant, number  of branches, root volume and dry matter yield and  partitioning to the leaves, stem and roots. All the data were subjected to Analyses of Variance (ANOVA) following the procedures outlined for completely randomized design (CRD). Significant treatment means were separated with the aid of F-LSD at 5% probability level. All statistical analysis were done using Genstat 7.1 version 2003 software. Results indicated that all the seed physical traits showed significant (P < 0.05) variation across the four locations (states). Seeds from Enugu (74.08%)  had the highest edible proportion followed by Abia (70.68%) and Rivers (66.65%). Anambra accession had the highest seed and pulp weight followed by Abia, Enugu and Rivers, respectively. Seed coat thickness was higher in accessions from Abia and Rivers States compared to others. The nutritional quality assessment revealed that ash, fat and moisture varied significantly (P<0.05) among the different accessions while carbohydrates, fibre and protein contents of the seeds did not differ across the locations.  The moisture and fibre contents showed significant (P< 0.05) differences in the boiled and fresh seeds. Fibre content was higher in the boiled seeds, whereas the fresh seeds had higher moisture content. The ash, carbohydrate, fat and protein contents were not influenced by processing.  All the proximate contents of the seeds across locations did not differ in their response to interaction of location and processing.  Location showed no significant effect on iso-leucine, leucine, phenylamine and tryptophane contents of the seeds. Seeds collected from Rivers, Enugu and Anambra States gave significantly (P< 0.05) higher histidine than those from Abia. Abia accession has the highest lysine content compared with those from other locations. Enugu and Rivers accessions gave significantly (P< 0.05) higher methionine than those from Anambra and Abia State. Enugu and Abia accessions recorded higher threonine content than Anambra and Rivers accession. The effect of processing on essential amino acids showed that the histidine, isoleucine, leucine, lysine, methionine, phenylamine, valine and threonine contents of the seeds were not influenced by processing. Except for tryptophane, all the other essential amino acids were found to be higher in the fresh seeds. The effect of location on non-essential amino acids showed that alanine, arginine, asparagine, glutamine and glutamic acid were significantly influenced by location while aspartic acid, glycine, proline, serine, trimethlisine and tyrosine did not vary among the locations. Seeds collected from Abia State gave significantly higher alanine and arginine contents than those from other locations. Asparagine content was significantly (P < 0.05) higher in seeds from Rivers and Abia than those from Anambra and Enugu. pGlutamine acid content of seeds from Enugu and Anambra was higher than those from Abia and Rivers. The effect of processing on the non-essential amino acid components showed that glutamine, glutamic acid and trimethlisine contents of the seeds varied significantly (P <0.05) with processing. Glutamic acid and trimethlisine contents were higher in the fresh seeds whereas glutamine was higher in the boiled seeds. Alanine, arginine, asparagine, aspartic acid, glycine, proline, serine and tyrosine did not differ in their response to processing. Field growth performance evaluation indicated that plant height, stem girth, number of branches and vine length were all significantly (P < 0.05) improved with increasing manure rate.  The 10 tonnes manure rate partitioned the greatest portion of the biomass to the shoot in all the accessions.